use blob.exists to check the GCS file

[liferoad]

Addresses #34792

Note: This wont fix the slowness when checking 50K GCD files exist. But this optimizes the speed slightly.

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[shunping]

Thanks for attempting to fix the issue.

I see you are trying to replace bucket.get_blob, called in _gcs_object, with blob.exists.

I took a look at the two function calls.

• bucket.get_blob
  • calling blob.reload inherited from _PropertyMixin at https://github.com/googleapis/python-storage/blob/v2.18.2/google/cloud/storage/_helpers.py#L216
    • calling client._get_resource at https://github.com/googleapis/python-storage/blob/v2.18.2/google/cloud/storage/_helpers.py#L300
• blob.exists
  • calling client._get_resource at https://github.com/googleapis/python-storage/blob/v2.18.2/google/cloud/storage/blob.py#L734

It seems that under the hood, both apis are calling the same client._get_resource, though the query parameters may be different. I am not sure if the change could make any performance improvement for the use case here.

Adding @cojenco and @andrewsg from GCS client library to chime in regarding any performance difference between bucket.get_blob and blob.exists.

[shunping]

I ran some tests on both apis, it does have some difference, though not big

from google.cloud import storage
import timeit

storage_client = storage.Client()

bucket = storage_client.bucket("shunping-test")

time_taken = timeit.timeit(
  lambda : bucket.get_blob("wordcount-output-00000-of-00001"),
  number=100)
print(time_taken)

blob = bucket.blob("wordcount-output-00000-of-00001")
time_taken = timeit.timeit(blob.exists, number=100)

print(time_taken)

6.079686500015669
5.889628666976932

[cojenco]

Thanks for attempting to fix the issue.

I see you are trying to replace bucket.get_blob, called in _gcs_object, with blob.exists.

I took a look at the two function calls.

• bucket.get_blob

  • calling blob.reload inherited from _PropertyMixin at https://github.com/googleapis/python-storage/blob/v2.18.2/google/cloud/storage/_helpers.py#L216

    • calling client._get_resource at https://github.com/googleapis/python-storage/blob/v2.18.2/google/cloud/storage/_helpers.py#L300

• blob.exists

  • calling client._get_resource at https://github.com/googleapis/python-storage/blob/v2.18.2/google/cloud/storage/blob.py#L734

It seems that under the hood, both apis are calling the same client._get_resource, though the query parameters may be different. I am not sure if the change could make any performance improvement for the use case here.

Adding @cojenco and @andrewsg from GCS client library to chime in regarding any performance difference between bucket.get_blob and blob.exists.

Thanks for tagging! That's right, both bucket.get_blob and blob.exists ultimately call client._get_resource, so the performance difference is likely negligible.

[github-actions]

Reminder, please take a look at this pr: @shunping

[shunping]

On a second thought, using blob.exists could reduce the returned payload as mentioned in the comment of the function, so it is more optimized for checking the existence of a blob. Given there is no regression on tests, I am approving the change.

[shunping]

LGTM!